diff --git a/pfbudget/core/manager.py b/pfbudget/core/manager.py
index 7fd3b08..fc832e1 100644
--- a/pfbudget/core/manager.py
+++ b/pfbudget/core/manager.py
@@ -101,10 +101,20 @@ class Manager:
                     categories = session.select(Category)
                     tags = session.select(Tag)
 
-                    rules = [cat.rules for cat in categories if cat.name == "null"]
+                    rules = [
+                        rule
+                        for cat in categories
+                        if cat.name == "null"
+                        for rule in cat.rules
+                    ]
                     Nullifier(rules).transform_inplace(uncategorized)
 
-                    rules = [rule for cat in categories for rule in cat.rules]
+                    rules = [
+                        rule
+                        for cat in categories
+                        if cat.name != "null"
+                        for rule in cat.rules
+                    ]
                     Categorizer(rules).transform_inplace(uncategorized)
 
                     rules = [rule for tag in tags for rule in tag.rules]
diff --git a/pfbudget/transform/nullifier.py b/pfbudget/transform/nullifier.py
index 4be4909..16106a4 100644
--- a/pfbudget/transform/nullifier.py
+++ b/pfbudget/transform/nullifier.py
@@ -15,7 +15,7 @@ class Nullifier(Transformer):
     NULL_DAYS = 4
 
     def __init__(self, rules=None):
-        self.rules = rules
+        self.rules = rules if rules else []
 
     def transform(self, transactions: Sequence[Transaction]) -> Sequence[Transaction]:
         """transform